1. Field of the Invention
The present invention is in the field of streaming tape drives that store data generated by computers and other digital data devices. More particularly, the present invention is directed to a method for calibrating a streaming tape drive to optimize the magnitude of the current applied to a write head.
2. Description of the Related Art
Magnetic tape is a popular medium for storing large quantities of digital data generated by computers and other digital data devices. Streaming tape drives utilize narrow (e.g., 1/4-inch) magnetic tape, and record multiple tracks of data in a generally continuous format on the tape. The digital data is provided as an input to the drive which converts the digital data into a format suitable for recording on the magnetic surface of the tape within the drive. Basically, the digital data are recorded on the tape by a write head as a plurality of magnetic flux changes which can be sensed by a read head. The data are encoded in accordance with a selected recording standard so that the data can be reproduced by the tape drive which records the data, and by other tape drives that operate in accordance with the recorded format.
The magnetic flux density recorded on a tape depends upon a number of factors, one of which is the magnitude of the current applied to the write head when the data is recorded. Ideally, the magnitude of the write current should be selected to be substantially equal to the peak current of the write head. As used herein, the peak current of the write head corresponds to the magnitude of the current that produces the maximum voltage magnitude when the recorded flux changes are sensed by a read head. A write current in excess of the peak current will not increase the magnitude of the voltage generated by the read head, and will in fact cause the magnitude of the voltage to decrease. Generally, magnetic write heads are specified in terms of their respective saturation currents. The saturation current typically will generate magnetic flux transitions that provide a read voltage that is approximately 95% of the maximum read voltage at the peak current. The following description will refer to the peak current of a magnetic write head.
Because of presently used mass production techniques, the commercially available write heads for streaming tape drives have a wide range of peak currents. For example, in an exemplary head specification, an acceptable saturation current may be specified that corresponds to a peak current in the range of 15 milliamperes to 30 milliamperes. It can be seen that a production tape drive that applies a fixed current to a magnetic write head will provide an optimal write current for only a limited number of write heads constructed in accordance with the specification. For example, a tape drive constructed to operate at a write current of 25 milliamperes will operate at less than the peak current for some of the write heads and will operate far in excess of the peak current for other write heads. As set forth above, operation above or below the peak current will result in output voltage from a recorded tape that is less than the maximum output voltage.
One solution to the above-described problem is to manually adjust the operating write current value for each tape drive, so that it corresponds to the peak current of a particular write head to be installed in the tape drive. Although this can be accomplished, the amount of time required to manually adjust each tape drive does not make the procedure economically feasible for production tape drives in which large quantities of tape drives are produced. Thus, a need exists for an apparatus and method for automatically adjusting the write current to an optimal magnitude for a particular write head in a tape drive.